1. Field of The Invention
This invention relates to an adapter used between a turning implement and a fluid tube fitting, whereby the fitting can be tightened to a precise torque setting.
2. Prior Developments
In the fields of high performance liquid chromatography and flow injection analysis miniature plumbing systems incorporating miniature fittings and small bore tubing are used to interconnect such components as pumps, valves, chromatography columns, and detectors. The tubing is secured, using special miniature fittings which usually consist of a hollow threaded screw and a ferrule. The ferrule fits onto the tubing, and as the hollow screw is tightened the ferrule is compressed into the associated cavity, which compresses the ferrule onto the tubing, forming a leaktight seal at pressures up to 10,000 psi. The hollow screw needs to be tightened to adequately compress the ferrule, giving a tight seal around the tubing and forming a leaktight connection between the miniature tubing and the component that is being plumbed to the tubing. If the hollow screw is not tightened enough, inadequate compression of the ferrule occurs allowing fluid to leak from the tubing-body interface. If the hollow screw is tightened too much, damage can occur to the screw threads or the head of the screw can break off leading to damage to the fluid component. Another problem called fluid premixing can also occur, which can compromise the analytical results.
In order to tighten the hollow screw or nut two methods are used. The traditional method involves hand tightening the fitting and then turning the screw an additional fraction of a turn with a wrench. The second technique utilizes plastic fittings with special ferrules which need only to be finger tightened to give a leak free seal up to several thousand psi. The problem with both of these methods is that the exact amount of torque applied when the hollow screw is tightened is not reproducible since the amount of torque that is applied by the human hand can vary, depending on the strength and manual dexterity of the user. Wrench tightening, which requires rotating a wrench a certain fraction of a turn using the naked eye, is also only approximate and can vary from user to user. Since the torque applied is directly related to the amount of compression of the ferrule onto the tubing, the compression also becomes irreproducible.
Commercially available turning implements have torque gauges built into the implement. Such implements come in either the form of a screwdriver or wrench, and use drive sockets or screwdriver bits for applying torque. Torque wrenches are used for higher torque applications while torque screwdrivers are usually used for low torque application. Neither a torque screwdriver or torque wrench can be used with miniature plumbing fittings since the tubing protruding from the end of the hollow screw would interface with the socket on the screwdriver or wrench.
The present invention eliminates the problem of protruding tubing by offering specially designed adapters which can grasp onto all common types of miniature fittings without interfering with the protruding tubing. The essence of the invention is the design of these fixtures which can accomodate a variety of torque adjustment devices such as a torque gauge screwdriver, torque wrench, and torque limiting screwdrivers and wrenches. The adapters can be used with both hand tightened and wrench tightened chromatography fittings, and to thus give the user the ability to accurately measure and apply torque to these various fittings used in high performance liquid chromatography and flow injection analysis.